Not Applicable
Not Applicable
This invention relates to a low-lift fork truck.
Low-lift fork trucks having an electric motor drive have become known in very different embodiments. They generally are composed of a load-carrying part which is held on a driving part so as to be adjustable in height to a limited extent. The driving part has a driving wheel centrally disposed on the longitudinal axle, which mostly is driven by a wheel hub drive. The driving wheel is supported in a steering bolster which, in turn, is pivotally supported about a vertical axis. The steering bolster is engaged by a drawbar the head of which contains actuating elements for the control of the drive and a lifting device which usually comprises a lifting cylinder which is coupled to the load-carrying part via appropriate means. The load-carrying part is composed of two parallel-spaced wheel arms which are interconnected via a rigid transverse member. Each of the wheel arms carries a forcing bar which, towards the free end, is coupled to a rocker which supports a load-carrying roller. At the drive end, the forcing bar is coupled to a linkage which when the lifting cylinder is operated is actuated, in turn, to displace the forcing bar and to move out or retract the load-carrying roller.
It is the object of the invention to improve such a low-lift fork truck in a way that the driving part may be designed to be smaller and more compact.
In the inventive low-lift fork truck, the lifting cylinder is disposed centrically to the pivotable axis of the steering bolster with the load-carrying part carrier, as a rigid member, connected by a hinge to the upper end of the lifting cylinder. Provided in the lower area of the driving part are two parallel levers which are hinged to the frame of the driving part at one end and to the load-carrying part carrier at the other. This gives the load-carrying part a guide in lifting or lowering the lifting cylinder. Although the hinge point of the levers on the transverse member describes an arc during a lift whereby a slight tilt of the load-carrying part occurs this motion is negligible, particularly when the hinge points of the levers, on the transverse element, are in a plane which is approximately vertical in the lifted and lowered positions. According to an aspect of the invention, the hinge point of the levers on the driving part preferably is in a plane which extends through the axis of the lifting cylinder and, hence, the pivoting axis of the steering bolster.
The centric disposition of the lifting cylinder has the exceptional advantage that only low flexural moments occur because the transmission of forces to the load-carrying part substantially takes place in the axis of the lifting cylinder. Therefore, the lifting cylinder may be designed to be relatively small. The arrangement of the lifting cylinder, in turn, results in a compact way of construction of the driving part.
According to an aspect of the invention, the load-carrying part carrier is defined by an approximately U-shaped bow the legs of which are rigidly connected to the transverse member and the web of which is hinged to the lifting cylinder via two parallel plates. This makes it possible to improve the transmission of forces by the fact that braces which are laterally connected to the transverse member laterally engage the legs of the bow.
Another aspect of the invention provides that the lifting cylinder, by means of its piston rod, bears onto the steering bolster and the load-carrying part carrier is hinged to the cylinder jacket and that a motor-driven pump unit is firmly connected to the cylinder jacket. In this embodiment, flexible-tube connections which, in addition, are continuously moved while the lifting cylinder is actuated, may be omitted. A unit comprising a motor pump and a tank, which is disposed in a single casing, may be provided which is connected to the jacket of the lifting cylinder in an appropriate way. Also, a very small tank may be provided where a change of the hydraulic oil is normally unnecessary. According to an aspect of the invention, the cylinder jacket and the casing for the motor-driven pump unit may also be formed integrally.
In the embodiment mentioned last, the piston rod bears onto the steering bolster and, therefore, will be turned along when the steering bolster is pivoted. It is quite imaginable to provide an appropriate bearing to prevent the piston rod from rotating. However, the rotation of the piston rod does not pose a problem, particularly if the lifting cylinder has adequately been designed for this purpose.